1. Field
Embodiments relates generally to a method for improving the performance of multicast and broadcast service and, more particularly, to a method and system for efficiently transmitting data, to which scalable image coding has been applied over a single frequency network.
2. Description of the Related Art
With the dramatic developments in computer, electronic and communication technology, a variety of wireless communication services have been provided over wireless communication networks. Accordingly, voice service-centered basic communication systems, which provide a wireless voice call service to the users of mobile communication terminals, have evolved into communication systems capable of providing an image data service and a variety of multimedia services.
Voice service-centric communication systems cannot meet rapidly increasing demands for service because transmission bandwidth is narrow and service charges are expensive. Furthermore, since there is an increased need for communication systems capable of efficiently providing Internet service due to the development of communication business and an increase in user demands for Internet service, Orthogonal Frequency Division Multiplexing (OFDM)-based wireless communication systems have been introduced.
Wireless communication systems are used to provide important services, i.e., Internet service, Voice over IP (VoIP) service, and streaming services. Recently, broadcast services are rapidly increasing. The broadcast services provide high-quality image data in real time using a Multicast and Broadcast Service (MBS) technique regardless of time and place.
MBS is capable of providing image services, i.e., a news service, a drama service, and a sports relay broadcast service, and data services, i.e., a radio music broadcast service and real-time traffic information. MBS is also capable of simultaneously transmitting a variety of channels at high transmission rates using a macro-diversity technique.
A mobile internet protocol television (IPTV) service provides high-image quality video and high-sound quality audio. The mobile IPTV service is an example of a broadcast service using MBS, and is emerging as a principal service of fourth-generation mobile communication systems. IPTV is a service which provides information, moving image content, and broadcasts to televisions (TVs) over an internet protocol (IP) network, i.e., the high-speed Internet. Mobile IPTV is integrated with two-way system operation enabling networking via TVs.
FIG. 1 is a diagram illustrating an example of the configuration of a typical mobile IPTV broadcasting network. FIG. 1 is a broadcasting network which provides services using a MBS technique.
Referring to FIG. 1, a base station 100 for providing mobile TV service provides user terminals 120 with the mobile IPTV service over a wireless communication network, i.e., a WiBro, 3GPP or LTE network, in conjunction with an STB-IPTV 110.
In order to improve the performance of a wireless access network, a variety of technologies and IPTV broadcasting network configuration and control technologies for the control of IPTV broadcast service are required. For example, in order to improve the performance of a wireless access network, a Single Frequency Network (SFN) and Fractional Frequency Reuse (FFR) may be utilized. Furthermore, examples of what is required by the IPTV broadcast service control technology are a Scalable Video Coding (SVC) technique using an adaptive module and an Adaptive Modulation and Coding (AMC) technique, multi-carrier technology for ensuring a multi-TV channel, and wireless link control technology in an MBS environment.
Of the above technologies, the SFN technique is a method of transmitting broadcast signals to adjacent areas at the same frequency in OFDM digital transmission. The SFN technique is chiefly used in terrestrial DMB broadcasting. The use of the SFN technique can reduce inter-cell interference attributable to the use of the same frequency and can also reduce the frequency of handovers. Thus, a high-quality mobile IPTV service is ensured.
FIG. 2 is a diagram illustrating the configuration of an MBS zone in a related art wireless communication system.
Referring to FIG. 2, the wireless communication system of the related art builds a single MBS zone using 7 base stations located in an area where broadcasting service is provided, in order to apply a macro-diversity technique. The term “MBS zone” refers to a specific area where the MBS service is provided. An area each base station provides service is referred to as a cell or a sector. An MBS zone may include one or more cells or sectors where one or more base stations provide MBS service.
A wireless communication network which is used to provide IPTV service in such an MBS zone may include, for example, an International Mobile Telecommunications-Advanced (IMT-Advanced) next generation mobile communication technology network, a 3rd Generation Partnership Project (3GPP) network, and a Long Term Evolution (LTE) network.
IMT-Advanced next generation mobile communication technology is intended to support a data transfer rate of 100 Mbps during high-speed movement at a speed equal to or higher than 60 km/h, and a data transfer rate of 1 Gbps at rest or during low-speed movement. IMT-Advanced also provides a demand-specific wired and wireless and broadcasting and communication convergence mobile multimedia service via personal portable terminals. IEEE 802.16 will now be described as a standard of IMT-Advanced technology.
The Institute of Electrical and Electronics Engineers (IEEE) is a U.S.-centric international standardization organization, and establishes an 802.16 family, which is called “Worldwide Interoperability for Microwave Access (WiMAX).” The IEEE 802.16 working group originally established a standard for point-to-point microwave transmission, introduced Orthogonal Frequency Division Multiplexing (OFDM) technology in order to ensure reliable transmission in a Non-Line-Of-Sight (NLOS) environment, and established IEEE 802.16-2004. IEEE 802.16-2004 is called “Air Interface for Fixed Broadband Wireless Access System,” and was established in 2004. The IEEE 802.16 working group established IEEE 802.16e-2005 (hereinafter referred to as “16e”), called “Mobile Broadband Wireless Access System” in which mobility was added to IEEE 802.16-2004. A so-called Wireless Broadband (“Wibro”) system is compatible with a 16e system. The Wibro system supports a bandwidth of 8.75 MHz, whereas 16e supports bandwidths of 3 MHz, 5 MHz, 7 MHz, 8.75 MHz, and 10 MHz. IEEE is working on the standardization of IEEE 802.16m (hereinafter referred to as “16m”), called “Advanced Air Interface with data rates of 100 Mbit/s mobile & 1 Gbit/s fixed.” In regard to 16m, a more evolved Enhanced Multicast and Broadcast Service (E-MBS) standard to which the MBS technique illustrated in FIG. 2 has been introduced in order to support broadcast service.
FIG. 3 is a diagram illustrating an example of a frame structure in compliance with IEEE 802.16 in a related art wireless communication system.
Referring to FIG. 3, in IEEE 802.16, each superframe includes 4 frames of the same size, and each frame includes 8 subframes. Each subframe may be assigned to any one of an uplink and a downlink. Although not shown in the drawing, each subframe includes 7 Orthogonal Frequency Division Multiplexing Access (OFDMA) symbols.
As shown in FIG. 3, when an E-MBS subframe is transmitted, each frame may be configured in a fixed pattern such that the E-MBS subframe is assigned to any one of 8 subframes.
As described above, a variety of schemes for efficiently utilizing a frequency band in order to efficiently provide an MBS service in a wireless communication system have been proposed. One of these schemes provides MBS using the above-described SFN technique.
When MBS is provided using the SFN technique, the Signal to Interference Plus Noise Ratio (SINR) value of users located in an SFN zone increases. Thus, high-data rate Adaptive Modulation and Coding (AMC) mode can be selected, increasing frequency efficiency. In contrast, base stations located in an SFN zone cannot flexibly utilize a frequency band. Base stations located in an SFN zone utilize the frequency band for the SFN zone in a fixed manner. For example, when the SFN technique is utilized, service is always provided over the frequency band. Even when there is no user in the SFN zone, service is always provided in the SFN technique. Furthermore, when data encoded by the Scalable Video Coding (SVC) technique is transmitted to all users located in the SFN zone, increasing overhead occurs. Increasing overhead occurs when data is encoded by the SVC technique in the SFN zone due to unusable data in the performance of a user terminal.